The invention concerns a bag for heating liquids, in particular, a bag for heating blood, and a bag heating means for heating cooled liquids, e.g. blood, to a temperature which is suitable for transfusion. A blood heating system which consists of a liquid heating bag and a bag heating means of this type is used for heating natural blood for transfusion purposes or for dialysis as well as for transfusion of blood plasma or other liquids.
Blood is usually kept at a temperature of approximately 4° C. Prior to use, the blood must be heated to body temperature of approximately 37° C. The blood which is used for transfusions must have a temperature of at least 28° C. and at most 40° C. In particular, in case of an emergency, the blood must be heated very quickly, since it is not possible to keep heated blood ready for possible emergencies. In case of an emergency, the blood must be heated quickly and also the handling of the blood heating system must be simple and straightforward. The stated temperature conditions must be kept irrespective of the flow rate of the blood through the blood heating system. This flow rate may be up to 5 liters per hour for infusions under pressure. To avoid overheating, the temperature of the bag heating means may only be slightly above the body temperature with the consequence that the bag heating means must provide a large heat exchanging surface to obtain sufficient heating capacity.
Prior art discloses bag heating means of various designs. One can differentiate between bag heating means for inserting a liquid heating bag, having a chamber which can be opened and which is closed during heating of the inserted liquid heating bag, and into which the liquid heating bag is inserted, and bag heating means for inserting a liquid heating bag into a gap formed between two heat exchanger plates which are fixed parallel to each other using fastening means. The bag heating means having a chamber which can be opened are relatively difficult to handle and are therefore suited for use in emergencies only to a limited extent.
A bag heating means for inserting a blood heating bag is disclosed in DE 1953991. This bag heating means comprises heating elements which form two substantially rectangular heat exchanger plates with one flat heat exchanging surface each. The heat exchanging surfaces of the heat exchanger plates are disposed opposite to each other at such a distance that a gap is formed between the heat exchanging surfaces for receiving a blood heating bag. The heat exchanger plates are mounted to each other on a first long side edge of the heat exchanger plates such that the heat exchanging surfaces are fixed parallel to each other. The gap is open along a second long side edge and two narrow side edges of the heat exchanger plates such that a blood heating bag can be introduced, e.g. from the second long side edge, into the gap. The gap has a width of approximately 6 millimeters to prevent compression of the inlet line and outlet line, i.e. to prevent squeezing off the flow. A gap with such a wide opening entails that the volume of the blood in the blood heating bag is also very large, such that the blood may be in contact with the heat exchanging surfaces via the blood heating bag. For dialysis applications, the extracorporeal blood volume must be as small as possible, and for applications as blood heating means, the residual volume remaining in the blood heating bag should be as small as possible to prevent waste of blood. For this reason, the use of this bag heating means is quite limited. The blood heating bag disclosed in DE 1953991 must be inserted into the bag heating means with a predetermined orientation. The use of the blood heating system is prone to errors, in particular, in case of an emergency.
US/2003/0099469A1 describes a further bag heating means for inserting a blood heating bag. This bag heating means comprises a gap between two heat exchanger plates. The gap is closed at two long sides. A blood heating bag is inserted into the bag heating means in a similar manner as a thread is introduced into the eye of a needle, thereby using an insertion tab. The blood heating bag has a flow volume formed from two flexible plastic foils which are connected to each other at four delimiting edges, wherein the flow volume has a flat trapezoidal basic shape which is delimited by the delimiting edges. The blood heating bag also comprises an inlet line opening and an outlet line opening, wherein the inlet line opening and the outlet line opening are disposed at a first delimiting edge, and an insertion tab is disposed at a second delimiting edge opposite to the first delimiting edge. The blood heating bag also comprises a liquid flow guiding seam formed by a connection between the plastic foils in the region of the flow volume. The insertion tab is made from a semi-rigid cardboard material and is mounted to the actual blood heating bag. One disadvantage of this blood heating system is the fact that the blood heating bag is produced from several materials. Production of the blood heating bag therefore requires several processing steps which causes great expense. Moreover, insertion of the blood heating bag into the blood heating means is very complex which consumes valuable time in case of an emergency.
It is the underlying purpose of the invention to provide a liquid heating bag and a bag heating means which eliminate the disadvantages of prior art, and in particular provide quick and straightforward handling.